The move adds uncertainty to the future of the project which has already faced years of delay.

Dozens of Nebraska landowners filed a notice of appeal to the Nebraska Court of Appeals. They are planning to contest a 20 November decision by the Nebraska Public Service Commission to approve a route through the state for Keystone XL.

The Nebraska Court of Appeals last week set some dates for the appeal, including a 14 February deadline for some documents and a 16 March deadline for appellants to file a brief.

TransCanada is monitoring the filing and its potential impact on the project, a spokesman said today.

The $8bn Keystone XL would transport crude from Alberta's oil sands to Steele City, Nebraska, which is already linked to Cushing, Oklahoma, and the southeast Texas coast.

The Nebraska Public Service Commission voted 3-2 to approve a Keystone XL route through the state, but not TransCanada's preferred 275-mile (443km) route. Rather it approved "a mainline alternative route."

Nebraska regulators last month rejected TransCanada's request to submit an amended application to address some issues related to the alternative route.

The Keystone XL alternative route would start at the Nebraska-South Dakota border and follow the same path as TransCanada's preferred route for 110 miles (118km). It then separates from the preferred route towards the southeast and then parallels the existing Keystone mainline in two stretches.

Opponents to the project say that the environmental impacts of the alternative route were not properly examined by state and federal agencies.

TransCanada first proposed Keystone XL in 2008 but it was delayed repeatedly. The administration of previous US President Barack Obama in 2015 blocked Keystone XL after years of review, citing environmental concerns.

The project was revived last year, receiving a cross-border permit from the Trump administration in March 2017.

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